1. Field of the Invention
The present invention relates to tilt tables and, more particularly, to pointing platforms which require tilting in two axes so that a line perpendicular to the surface of the platform can be made to point anywhere within a predetermined conical area.
2. Description of the Prior Art
There are a number of devices available in the prior art to provide pointing in any direction, usually with use of two mutually interactive hinges. A simplified example of such a prior art arrangement is shown in FIG. 1.
In FIG. 1, a horizontally arranged first table 10 is shown to be rotatable in the direction of arrows 12. Mounted in the center of table 10 is a bracket 14 which carries a second table 16 shown by rotatable in directions shown to be arrows 18. It will be seen that an axis 20 perpendicular to second table 16 can be made to point in almost any direction by a combination of rotating table 10 and table 16.
There are problems with the operation of devices constructed similar to the structure of FIG. 1 due to the requirement that mounting bracket 14 requires a certain length so that table 16 does not interfere with table 10 at any point in the positioning thereof. In the interest of maintaining a required stiffness, this added length results in a weight penalty. There is also a problem when apparatus like FIG. 1 is to be used in space since the whole mechanism needs to be carefully locked to prevent damage due to forces occurring during the extreme conditions encountered at takeoff. It will be observed that the length of shafts 11 and 14 provide a lever arm that can produce a severe moment on the platforms 10 and 16 when the enormous forces acting during lift-off of a satellite occur. This also requires that the pointing platforms be robust and heavy. Another problem is the conduction of heat since the pivots used in the apparatus like FIG. 1 are generally poor heat conductors, and therefore, in situations where heat conduction is necessary, the spacecraft needs greater ability to limit temperature.